Differential Diagnosis for the 3 mm Nodule
- Single most likely diagnosis
- Benign cyst or pseudocyst: The nodule's small size, location, and evolution over time from a potentially cystic to a solid appearance could suggest a benign cyst or pseudocyst, especially given the lack of aggressive features or significant growth.
- Other Likely diagnoses
- Reactive lymph node: The location anterior to the psoas muscle could suggest a reactive lymph node, especially if there were any inflammatory or infectious processes in the vicinity, although the history provided does not strongly support this.
- Vascular malformation or aneurysm: Although less common, small vascular anomalies could present as solid nodules, especially if they have thrombosed or undergone other changes over time.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Metastasis from the chromophobe RCC: Despite the small size of the primary tumor and its favorable histology (T1A, no sarcomatoid features, no necrosis), the possibility of metastasis, although low, cannot be entirely excluded. Metastases can sometimes present as small, solid nodules.
- Lymphoma: Although rare, lymphoma can present with small nodules in various locations, including near the kidneys, and would require prompt diagnosis and treatment.
- Rare diagnoses
- Adrenal rest tumor: If the nodule is actually related to the adrenal gland, an adrenal rest tumor could be considered, although this would be uncommon and typically associated with other clinical findings.
- Extra-adrenal paraganglioma: These are rare neuroendocrine tumors that can occur in various locations, including near the kidneys, but would be an unusual diagnosis for a small, solid nodule without specific clinical or biochemical findings suggestive of a paraganglioma.